1. Field of the Invention
The present invention relates to a waveguide, a method of manufacturing the same, and an electromagnetic wave analysis apparatus. In particular, the present invention relates to a waveguide for electromagnetic waves in frequency bands from a millimeter wave band to a terahertz wave band (30 GHz to 30 THz) (hereinafter referred to as terahertz waves), the waveguide configured to also be an oscillation device or a detection device, and methods for manufacturing the same.
2. Description of the Related Art
In the frequency band of terahertz waves, there are absorption peaks of many organic molecules in biological materials, medicines, electronic materials, and the like stemming from the structures and states thereof. Further, the terahertz waves easily penetrate materials such as paper, ceramic, resin, and cloth. In recent years, research and development have been conducted on imaging technology and sensing technology which make use of such characteristics of terahertz waves. For example, application thereof to a safe fluoroscopic apparatus to replace an X-ray apparatus, to an in-line non-destructive inspection apparatus in a manufacturing process, and the like is expected.
As a current injection type terahertz waves light source, a structure is under study, which uses an electromagnetic wave gain based on intersubband transition of electrons in a semiconductor quantum well structure. Appl. Phys. Lett. 83, 2124 (2003) proposes a terahertz waves band quantum cascade laser (QCL) in which double-side metal waveguides (hereinafter also referred to as DMWs) which are known as low loss waveguides are integrated as resonators. This device attains laser oscillation around 3 THz by light confinement at a high level and low loss propagation due to causing terahertz waves that are emitted by stimulated emission to be guided in a surface plasmon mode to a resonator structure in which metal is placed above and below a gain medium formed of a semiconductor thin film at a thickness of about 10 μm.
The DMW may cause an increase of edge reflection or beam pattern divergence due to mode mismatch between the waveguide and a space. Therefore, from viewpoint of application, there is a task of efficient use and handling of a beam. Concerning this, OPTICS LETTERS, VOL. 32, ISSUE 19, PP. 2840-2842 (2007) proposes a method of improving extraction efficiency and directivity by disposing a silicon lens at an end of the waveguide, but this method has practical problems such as being physically and mechanically unstable and requiring an additional member. Therefore, Japanese Patent Translation Publication No. 2010-510703 discloses an example in which a horn antenna is integrated. However, the structure can hardly be said to have sufficient physical and mechanical stability, and directivity of the electromagnetic wave may be tilted from an optical axis of the waveguide. Therefore, there is a room for improvement of frequency stability and handling of the electromagnetic wave.